Continuous feeding of scrap into electric furnaces supplied with alternating current is known, as are furnaces supplied with direct current.
However, in furnaces supplied with alternating current, the asymmetry of the arcs, which can be corrected partially as a result of electrical unbalance, gives rise to an unbalance between the three high-voltage supply phases which is incompatible with the requirements of the electrical energy supplier. This disadvantage does not arise in furnaces supplied with direct current.
Moreover, in arc furnaces the electrodes are normally arranged in the center of the vault, and the aim is to keep the arcs exactly vertical in the axis of the shaft, in order as far as possible to prevent localized overheating of the walls attributable to deflections of the arcs. However, it is difficult to introduce the scrap into the hottest zone, i.e., in practice, at the melting center located in the middle of the electrodes.
Although it has been proposed to use hollow electrodes serving as feed tubes, this technique makes the production of the electrodes more complicated and, in any case, can only be used with a raw material in divided form, and not scrap.